In recent years, photosensitive resins such as photoresist, photosensitive polyimide and the like have been widely used in the semiconductor industry, for formation of IC or ultrafine circuits (e.g. LSI) or for the insulation film or protective film in a package to be processed. Photosensitive resins have a feature in that they can form a resin pattern of high precision by using a relatively simple apparatus. In particular, positive photoresists using a diazoquinone or the like as a photosensitive material and a phenolic novolac resin as a base, can form a pattern of excellent resolution because they cause no swelling during development. Further, the positive photoresists use an aqueous alkaline solution as the developing solution and accordingly are superior in safety. Owing to such various features, the positive photoresists are in wide use for production of the above-mentioned fine circuits of semiconductor device, etc. Also in the photosensitive heat-resistant resins (e.g. photosensitive polyimide) used for the insulating film or protective film of a semiconductor device, positive photosensitive heat-resistant resins having features such as high resolution, no environmental pollution of developing solution used, and the like have been developed similarly to the above photoresists (see, for example, JP-A-64-60630 and JP-B-1-46862) and are drawing attention as a resin for use in the insulating film or protective film of a highly integrated semiconductor device.
Most positive photosensitive resin compositions are formulated by combing an alkali-soluble polymer and the above-mentioned diazoquinone compound as a photosensitive material. The diazoquinone compound is insoluble in an aqueous alkaline solution at unexposed portions but, when subjected to light exposure, gives rise to chemical change and becomes soluble in the aqueous alkaline solution. Therefore, by utilizing the difference in solubility between exposed portions and unexposed portions and removing the exposed portions with an aqueous alkaline solution, a coating film pattern consisting of the unexposed portions alone can be formed.
The aqueous alkaline solution used as a developing solution is ordinarily an aqueous solution of tetramethylammonium hydroxide (hereinafter referred to as TMAH). A photoresist using an ordinary phenolic novolac resin as a base can be developed satisfactorily with this aqueous TMAH solution; however, in developing, for example, a photosensitive resin composition using, as a base, a polybenzoxazole precursor, as disclosed in JP-B-1-46862, scum of development remains at the exposed portions (though these portions need be dissolved and removed completely), which has given a low resolution.
As well known, there can be mentioned, as factors used for evaluation of a photosensitive resin, sensitivity (minimum exposure energy required for pattern formation), resolution (ultimate pattern fineness at which pattern formation is possible) and contrast (difference in solubility in a developing solution between exposed portions and unexposed portions). When attention is paid to the contrast, the base polymer contained in a positive photosensitive resin composition composed of an alkali-soluble polymer and as diazoquinone compound is soluble in an aqueous alkaline solution both before and after light exposure; therefore, even the polymer in the unexposed portions is dissolved during development. Consequently, in the development using a conventional alkali developing solution, the film thickness of unexposed portions has been decreased and no satisfactory contrast has been obtained. To alleviate this drawback, a method has been known which comprises adding a solubility-controlling agent (e.g. heterocyclic compound or cyclic acid anhydride) to a photosensitive resin composition to suppress the solubility of the resin in the resin composition (JP-B-48-12242 and JP-B-56-30850). This additive, however, remains in the resin after development. As a result, the additive has reduced the heat resistance, mechanical properties, etc. of the photosensitive resin, which has made difficult the use of the photosensitive resin in applications such as insulating film of a semiconductor device and the like.
Use of a developing solution for photosensitive resin as disclosed in JP-A-3-104053 can achieve an improved film-thinning ratio but has had a problem of reduction in sensitivity and resolution.